The energy of the waves is greatest in open sea far from shore. Closer to shore, wave energy is dissipated due to bottom friction and diffraction effects. Many wave energy converters use floats that bob up and down on the wave with relation to the seabed, this movement may be used to generate electricity. However these type of energy converters intrinsically only harvest a small proportion of the wave's energy even if erected in open sea. A wave's energy could be regarded as linear, perpendicular and/or parallel to the gravity of the earth. The energy that is parallel to the earth's gravity can be looked at as alternating in direction. Many methods for converting wave energy to electrical energy, particularly float based systems, have low efficiencies when attempting to convert alternating linear energy to the unidirectional rotation of a generator shaft.